The crossrams in 68 used on the Hemi dart were old stock from 1964. My magnesium crossram is legit for a 68 Dart but dated 64, by 68 the remaining inventory was available mostly aluminum, the magnesium crossrams were produced in lower numbers. I am thinking A/MP, but Pro Stock for a year or two is possible, we both could be right. For it to run Pro in 1972 I think the body would have needed updating I believe the rule was within two years of production for Pro. Following your work closely very intrested in the build.